Process of tanning with aldehydes



Patented Sept.'13, 1938 UNITED STATES PATENT. OFFICE Harold G. Turley, Moore-stown, N. 1., and M0. Somervllle, Philadelphia, Pa", asslgnors to R4'5hm-& Haas Company, Philadelphia, Pa.

No Drawing. Application June 20, 1936, Serial No. 86,338

1 Claims. (c1. 149-5) This invention relates to an improved process for tanning raw hides and skins, and particularly to simplification and improved control of the.

process of tanning with aldehydes.

It has long been known that raw hides and skins may be converted into leather by treatment v with aldehydes, especially formaldehyde. In general the skins are prepared for formaldehyde tannage by first removing the hair with lime, sodium sulfide, etc., after which the strong alkali is removed by the operation of bating or puering. The resulting skins usually have a pH of the range of 7 to 9 and in this condition'are ready for tanning with formaldehyde. In a second method the skins, after unhairing, are pickled in a solution of sulfuric acid and salt, in which case it is necessary to neutralize the strong acid. This is accomplished either by the addition of a. strong base, such as sodium hydroxide, or by employing the Well known action of buffer salts.

In establishing a uniform pH throughout the skins by these means frequently a long time is required to insure that the alkali penetrates the innermost fibers. The present invention is an improvement in tanning skins prepared by the second of these methods whereby the neutralization is eliminated as an independent step and combined with the formaldehyde treatment.

It has been discovered that skin's may be tanned with aldehydes on the acid side of the iso-electrlc point and furthermore that the process of tanning may be carried out simultaneously with the step of adjusting the pH by adding to the aldehyde a sufiicient quantity of buffersalt to establish the proper pH, viz: 4.0 to 5.0.

It is an object of this invention to provide a process for tanning pickled skins directly with aldehydes. It is a further object to provide a simple and easily controlled process thus insuring uniformity and duplicability of results so that the usefulness of aldehyde tannage is greatly extended. Another object is to provide a simple aldehyde tannage which will permit the production of a good white leather and also of leather which has an exceptionally smooth, fine grain.

The invention is carried out by treating the pickled skins in a brine solution with a mixture of a buffer salt and an aldehyde capable of combining with the hide substance to produce leather.

In this way the pH'is rapidly adjusted to the proper range and as a result the tanning reactions proceed more rapidly and uniformly than is possi- Die by older methods. When the tanning is completed, theskins are thoroughly washed and fatliquored in the customary manner.

I phoric, etc.

Various buffer salts may be used. These are principally the alkali metal salts of weak organic or inorganic acids such as acetic, citric, phos- The actual value of the pH used will vary somewhat with the type of skin, the desired result and the time required for complete tannage and these factors must be considered in determining the amount and type of buffer necessary to produce the desired pH. The speed of aldehyde tanning increases as the numerical value of the pH increases and for complete tannage with formaldehyde in about twenty-four hours the pH should be adjusted to 4.0 or slightly higher. Although we prefer to carry out this tanning process by the simultaneous treatment of the pickled skin with the aldehyde and buffer salt, on the acid side of the iso-electric point, good results may also be obtained at pH values as high as 7.0. In the latter case the upper limit of. the pH will be determined by the appearance of the finished leather and should not be so high that a drawn or otherwise unsatisfactory grain is obtained. In all cases where the leather is to be subjected to further tanning by other agents, as for example according to the method of our United States Patent No. 2,029,088, January 28,

treatment of the skins with the aldehyde and buffer under such conditions that the tannage takes place at a pH of 4.5 to 5.0,

Formaldehyde is the most suitable aldehyde for use in this process, particularly when white leather is desired. However, other reactive aldehydes such as crotonaldehyde may also be employed under the same conditions.

This invention is illustrated by the following examples but is not limited to the exact ingredients, proportions and temperatures shown as it mixture of five pounds of egg yolk and two and one-half pounds of neats-foot oil, and horsed 1936, we prefer to carryout the simultaneousv I overnight. Next day they were set out and hung to B5 sammied, staked out, and finished as usual;

Example 2 One hundred pounds of pickled calfskins was sixteen pounds of 30% formaldehyde was added.

The pH of the resulting liquor was 5.5.. The skins were drummed for five hours and allowed to lie in theliquor overnight. Next day they'were horsed. set out and shaved, thoroughly washed and fatliquored with four pounds or a good quality sul- 15 'fonated neats-foot oil. After horsing overnight,

they were set out, crusted, and finished in the customary way.

Example 3 salt. While the drum was rotating, a solution of forty poundsof sodium acetate in one hundred twenty pounds of 30% formaldehyde was run in.

The pH of the resulting liquor was 4.75. The

skins were drummed for five hours and allowed to remain in the liquor overnight. Next day the drum was run one hour and the tannage supplemented by subsequent treatment with alum of fortylper cent. basicity and a synthetic tanning agent. 1

Example 4 One hundred pounds ofv pickled capeskins was placed in a drum with two hundred pounds of water and ten pounds of common salt. Ten pounds of crotonaldehydewas added and the drum run five minutes, then a mixture of ten pounds of sodium acetate and one and one-half pounds of glacial acetic acid was added. The pH of the resulting liquor was 4.5. The drum was run intermittently for forty-eight hours, then the skins were washed thoroughly and fatliquored with twelve-pounds oi. sulfonated cocoanut 011.

After horsing overnight, they were hung to dry in a cool room, and finished as usual.

Example 5 One hundred pounds of pickled sheepskins was placed in a drum with two hundred pounds of water'and ten pounds of common salt. A mixture of .ten pounds of 37% formaldehyde, six pounds of disodium phosphate, and three-quarters of a pound of citric acid was added. The pH of the resulting liquor was 4.25. The drum was run intermittently for twenty-four hours. The liquor was drained oil, the skins thoroughly washed, and i'atliquored with two per cent. of sulfonated 0 olive 011. At the end of the fatliquoring operawhile crotonaldehyde gives a more creamy shade.

tion, a white pigment was added. The skins were horsed' overnight, set out, hung to dry in a cool place, and finished as usual.

The properties of leather prepared according I 05' to these examples can be varied through wide limits by proper selection of pickled'skins and by changing the conditions of processing. In all cases where formaldehyde is the tanning agent, white leather with a smooth grain is produced,

dry in a cool room. When dry, they were These reactions are carried out at ordinarytemperatures for tannery operation, that is usually between 60" and F. It is advantageous in some cases to raise the temperature towards Leather prepared according to these methods is resistant to water as hot as 180 F.

This process can be extended to a great variety of dififerent types of pickled skins, as well as those specifically mentioned in the examples; for example, to furskins, buckskin, suede, calfskin, pigskin, reptile skins, horse hides and the like.

Since all special steps designed to prepare the pickled skins for aldehyde tannage, according to the usual practice, are eliminated by the present invention, a considerable amount of time is saved and a' much simpler and more easily controlled method is provided.

We claim:

1. In the process of manufacturing leather the step which comprises treating the pickled skins directly, and without first depickling simultaneously with a bufier salt and an aldehyde capable of combining with the hide substance.

2. In the process of manufacturing leather the step which comprises treating the pickled skins amounts suflicient to establish a pH approximately equal to that of the iso-electric point of the hide substance.

4.111 the process of manufacturing leather the step which comprises treating the pickled skins directly, and without first depickling simultaneously with formaldehyde and a bufier salt in amounts suflicient to establish a pH approximately equal to that of'the iso-electric point of' the hide substance. I v

5. In the process of manufacturing leather the step which comprises treating the pickled skins directly, and without first depickling simultaneously with formaldehyde and a buffer salt in amounts sufficient to establish a pH of from 4.0 to 5.0.

6. In the process of manufacturing leather the step which comprises treating the pickled skins directly, and without first depickling simultaneously with formaldehyde and sodium acetate in amounts sufllcient to establish a pH approximately equal to thatof the is0-electric point of the hide substance.

7. In the process of manufacturing leather the step which comprises treating the pickled skins directly, andwithout first depickling simultaneously with formaldehyde and sodium citrate in amounts suflicient to establish a pH approximately equal to that of the iso-electric point of the hide substance.

HAROLD G. TURLEY. IAN c. SOMERVILLE. 

